1. Field of the Invention
This invention relates to a curable silicone composition, and more particularly it is concerned with a curable silicone composition that comprises an organopolysiloxane having a fluorine-containing substituent and is useful for forming a film having a small surface energy.
2. Description of the Prior Art
Uses of curable silicones include, for example, release agents used in relation to pressure sensitive adhesives. The pressure sensitive adhesives are used in the form of, for example, rolled pressure-sensitive tapes and pressure-sensitive labels. Since the pressure-sensitive tapes must be unrolled when used, a coating with release properties is previously applied on the back surface of the tape so that they can be smoothly unrolled and also the pressure-sensitive adhesive may always remain on one surface of the tape. As for the pressure-sensitive label, a coating with release properties is applied on the surface of its support so that it can be smoothly peeled from the support when used and also no pressure-sensitive adhesive may remain on the support. Such a coating with release properties is required to have a sufficient cohesion by which the coating is strongly adhered to the back surface of the tape or to the support and may not migrate to the pressure-sensitive adhesive. Known as curable silicones excellent in such release properties are those mainly composed of an organopolysiloxane containing a fluorine-containing substituent represented by the formula: C.sub.n F.sub.2n+1 CH.sub.2 CH.sub.2 --where n is an integer of 1 or more (Japanese Unexamined patent Publication (KOKAI) Nos. 225,581/1987 and 320/1988).
In recent years, pressure-sensitive adhesives mainly composed of dimethylpolysiloxane are used in wide purpose because of their thermal resistance, cold resistance, chemical resistance and electrical insulating properties. Because of their non-toxicity, they are also used in the field of medical use. The pressure sensitive adhesives of this type, however, have so strong adhesion that the release agents comprising the conventional curable silicones may have insufficient in the release properties to be imparted. In particular, preservation for a long term of the tape or label that employ the pressure sensitive adhesive mainly composed of dimethylpolysiloxane may result in remarkable increase in peel force which is needed when the tape is peeled from its back surface or when the label is peeled from the support. Consequently, destruction of a pressure-sensitive adhesive layer and a release agent layer may occur when they are peeled, so that the tape or label may become of no use. In this respect, no satisfactory release properties can be attained even in the case of the above release agents disclosed in the Japanese Unexamined patent Publication (KOKAI) Nos. 225/581/1987 and 320//1988.